Chloroethene, commonly known as vinyl chloride monomer (VCM), is one of the world's major commodity chemicals. It is used in the manufacture of polyvinyl chloride (PVC), one of the oldest and most important polymers.
The first commercial process for large-scale production of chloroethene was developed in the 1930's. It involved the reaction of acetylene with hydrogen chloride. EQU C.sub.2 H.sub.2 +HCl.fwdarw.C.sub.2 H.sub.3 Cl (1)
U.S. Pat. No. 2,779,804 disclosed such a process. The acetylene feedstock for this method was manufactured by the reaction between calcium carbide and water. The disadvantages of this process were the high cost and scarcity of acetylene.
In the 1950's, a second commercial process was developed using ethylene as well as acetylene. Ethylene is first chlorinated by mixing it with pure chlorine gas, yielding ethylene dichloride, C.sub.2 H.sub.4 Cl.sub.2 (EDC) . EQU C.sub.2 H.sub.4 +Cl.sub.2 .fwdarw.C.sub.2 H.sub.4 Cl.sub.2 ( 2)
The ethylene dichloride is then subjected to high temperatures in order to crack it, producing C.sub.2 H.sub.3 Cl as a product and HCl as a byproduct . EQU C.sub.2 H.sub.4 Cl.sub.2 .fwdarw.C.sub.2 H.sub.3 Cl+HCl (3)
To recover its chlorine the HCl is used to hydrochlorinate acetylene, as shown in equation (1). U.S. Pat. No. 3,506,727 disclosed this process. The need for high-cost acetylene remains as a disadvantage of this second commercial process.
The commercial process that is currently employed by major VCM producers is a balanced process. It occurs in three basic steps: direct chlorination, pyrolysis, and oxychlorination. Ethylene is chlorinated with pure chlorine gas to produce EDC, as shown in equation (2) above. EDC is then cracked to produced vinyl chloride monomer and HCl, as shown in equation (3) above. HCl produced in EDC cracking is combined with ethylene and oxygen in an oxychlorination step that produces additional EDC and the byproduct water. EQU 2 HCl+C.sub.2 H.sub.4 +1/2O.sub.2 .fwdarw.C.sub.2 H.sub.4 Cl.sub.2 +H.sub.2 O (4)
The EDC produced in oxychlorination is recycled for pyrolysis to manufacture additional vinyl chloride, while the water, after wastewater treatment, is discharged into the environment. U.S. Pat. Nos. 3,504,043; 5,175,382; 5,099,085; 4,587,230; and 3,799,998 disclosed such a process.
The primary disadvantage present in this commercial process is the cost and energy efficiency of feedstock. Ethylene, which is employed in the oxychlorination step to recover the chlorine value from HCl, is a relatively expensive feedstock. The gases released from the oxychlorination vent also contain more than 100 ppm of vinyl chloride monomer (VCM), which has been shown to be an atmospheric health hazard. In addition, coking of the furnace tubes in the plant increases significantly with the more severe cracking conditions. Plants using this process must dispose of significant amounts of chlorinated hydrocarbon waste.
Several processes have been developed to use cheaper feedstocks for vinyl chloride production. U.S. Pat. Nos. 5,097,083 and 4,300,005 proposed the use of methane or ethane as feedstocks. Methods designed to reduce coking and promote cracking in the furnace have been disclosed in U.S. Pat. Nos. 5,210,345; 4,380,682; 4,590,317; 4,590,318; 4,584,420; and 4,225,520.
Various other processes for the production of vinyl chloride have been disclosed. U.S. Pat. No. 2,681,372 disclosed vinyl chloride production from C.sub.2 H.sub.4. U.S. Pat. No. 4,256,719 disclosed a process for the production of vinyl chloride without the consumption of elemental chlorine produced by electrolysis.
In commerce, 1,2-dichloroethenes are used as feedstocks for the production of tri-and tetra-chloroethenes. They are obtained as unwanted byproducts from other chlorination processes and, therefore, are not deliberately produced in large quantities. 1-dichloroethene is used to produce 1,1, 1-trichloroethane and poly (vinylidene chloride). It is manufactured by cracking 1,1,2-trichloroethane, a waste byproduct from the existing VCM process. Trichloroethene is used as a solvent for extraction or vapor degreasing. It is produced by chlorinolysis and oxychlorination processes.
Chloromethanes are important chemicals. They are used not only as industrial solvents but also as chemical intermediates. Chlorinated methanes are produced by thermal chlorination of methane. Byproduct HCl is recovered and sold as concentrated hydrochloric acid, if its market is available. HCl can also be disposed of, for example, by reacting with methanol to produce additional CH.sub.3 Cl.
It is therefore an objective of the present invention to provide a new method for the production of chloroethene that minimizes or eliminates the disadvantages of the existing methods. Other objectives and advantages of the invention will become apparent film the following description and the accompanying drawings: